The present invention relates to a developing member for a developing apparatus used in electrophotographic copy machines and printers, the developing apparatus employing a monocomponent developer comprising toner only.
Conventional developing apparatus which use monocomponent developers are known to supply non-magnetic toner to the surface of a developing roller that functions as a developing member and form a thin layer of charged toner on the circumference of the roller via pressure applied by a blade, this thin layer of charged toner making direct contact with the surface of an electrostatic latent image to produce a toner image.
U.S. Pat. No. 3,754,963 discloses a developing apparatus having a developing surface of minutely refined graphite particles dispersed in a resin.
However, the conductive developing roller achieves poor image density gradation and highly detailed, high density blind spot reproducibility is also poor. Further, when pin hole defects occur on the photosensitive member due to the abnormally strong electric field produced between the grounded photosensitive member and the charged developing roller or when a charge is discharged from the end portion of the developing roller, the bias voltage supplied to the developing roller leaks therefrom, thus reducing the bias voltage, generating uneven density, grainy fog or image dislocation and leading to discharge-induced damage to the photosensitive member.
In contrast, when a highly insulated developing member comprising only a dielectric material or developing member incorporating a minimum of conductive particles is used, density remains unsatisfactory and reproducibility of fine lines and blind spots is poor in spite of the excellent reproducibility of density gradations.